This background discussion will be directed to the patterning of textile substrates having a pile surface, and, accordingly, for convenience, will use floor coverings as the source for specific examples. However, the techniques described herein are not limited to such surfaces, and are intended to apply, as appropriate, to other substrates comprised of textile fibers that are woven, non-woven, knitted, bonded, or otherwise entangled or attached to provide a cohesive, structurally integrated textile.
With respect to colored textiles useful for floor coverings, the coloring or patterning process can be thought of as belonging to one of two classes: processes that apply dye to the constituent yarns prior to substrate or pile surface formation (“yarn-dyed” processes), and processes that apply dye to the substrate after the substrate (and the pile surface) has been formed (“substrate-dyed” processes). For each class, it is possible to further distinguish the various dyed or patterned textile products available in the market, and particularly, floor covering products. While the following discussion will refer to carpet as representative of such products, it should be understood that rugs, carpet tiles, mats, and other floor covering products are intended to be included in the discussion as if specifically mentioned, unless a contrary intent is explicitly stated or is inherently appropriate.
Historically, dyed carpets were almost exclusively produced by various yarn-dyed processes, in which the yarns were dyed the desired color prior to a weaving or tufting operation in which the colored yarns were formed into a carpet. At the present time, two processes appear dominant in the manufacture of yarn-dyed woven carpets: Wilton and Axminster. In the former case, a variety of colors may be used, but because the yarn is used in uncut form, all colors found in the pattern must be transported across the back of the carpet, regardless of the location or extent to which they are employed in the pattern. Accordingly, while a relatively high level of pattern detail and definition can be achieved, the number of colors that can be used within the pattern is limited by the practical burdens associated with having to supply and accommodate each color yarn at all times, regardless of its use within the pattern. An Axminster-woven carpet, on the other hand, uses cut yarns that are placed within the weave. Using this technique, yarns of many colors may be used, but pattern detail and definition are generally less than that found in Wilton-weave carpets. Of course, in either case, the manufacturing process is time consuming and costly.
Where tufted, rather than woven, carpets are produced, it is necessary to hide yarns not required in the pattern at each location in order to maintain the desired color at that location on the carpet. Because having many colors available would require the hiding of a considerable number of yarns throughout the carpet, tufted carpets are capable of exhibiting significant pattern detail and definition, but tend to be limited in terms of the number of colors that can be displayed.
More recently, carpet manufacturers have attempted to develop various processes in which an undyed or uncolored substrate may be patterned through the application of dye to the substrate surface. Because such processes generally allow use of a stock substrate that can be patterned quickly in accordance with customer demand, and thus provide significant manufacturing economy and flexibility, carpet manufacturers have maintained a strong interest in developing and improving such patterning processes.
Generally, such “substrate-dyed” processes have evolved along three different approaches. In a first approach (the “drop-on-demand” approach), the dye or colorant is applied directly from valve applicators positioned over the textile substrate to be patterned. In an example of one such system, a valve is opened when the dye or colorant is to be dispensed onto the substrate, and is closed when the requisite quantity of dye has been delivered to the appropriate predetermined area of the substrate.
In one configuration of such a device (referred to hereinafter as the “DOD” device), a print head containing a plurality of individual dye nozzles or applicators is traversed across the path of a substrate to be patterned. A plurality of dye reservoirs are generally used, each reservoir supplying dye of a respectively assigned color to one or more nozzles to provide for multi-color patterning. A given nozzle therefore dispenses dye of a pre-determined color, and only dye of that color (until the machine is reconfigured, the applicators cleaned, etc.), at one of several pre-set quantity levels affecting all colors, in accordance with electronically-defined pattern data. Such data, in the form of “on-off” instructions, are directed to selected nozzles to dispense dye of the various desired colors onto the substrate as the print head is traversed across the width of the substrate and the substrate is sequentially indexed forward, thereby allowing the dye nozzles comprising the print head to trace a raster pattern across the face of the substrate and dispense dyes of the desired colors on any desired area of the substrate dictated by the selected pattern.
This traversing motion is believed to have two consequences affecting the machine's ability to create a precisely formed line in a direction parallel to conveyor motion. The first involves the possibility that the traversing motion across the width of the substrate to be patterned introduces a velocity component in the cross-conveyor direction that may result in an elongation of the dispensed drops in the direction of the traversal. The second involves the fact that creation of such a line involves the ability to actuate and de-actuate the dye dispenser at the exact time necessary to form a series of pixels that are in precise alignment as the dispenser is moving perpendicular to the line being formed. Perhaps because of one or both of these possible effects, the pattern features produced by this type of DOD device are known to be significantly anisotropic (i.e., direction-sensitive).
In a second approach (the “recirculating” or “RECIRC” approach), the individual dye applicators are also associated only with a given color, and the applicators also may be arranged in rows, perhaps in a series of parallel rows arranged in spaced relation along the path of the moving substrate. However, rather than dispensing dye only when required by the pattern, the applicators in this re-circulating approach are always “on” and continuously generate a stream of dye that is directed towards the surface of the moving substrate, but that stream is normally diverted into a catch basin associated with each row by individual streams of a control fluid (e.g., air). Actuation or de-actuation of such applicators involves, respectively, de-actuation or actuation of the corresponding control fluid. Accordingly, the dye stream can reach the substrate only when it is not diverted onto the catch basin by the intermittently-actuated (i.e., actuated in accordance with pattern data) transverse stream of air or other control fluid for a time interval sufficient to dispense the quantity of dye (which may vary considerably from color to color) specified by the electronically defined pattern data. Separate sets of applicators and corresponding catch basins are used so that dye that is directed into a specific catch basin can be collected and re-circulated to the row of dye applicators assigned to that color dye. Some details of such a device are discussed below, as well as in a number of U.S. Patents, including commonly-assigned U.S. Pat. Nos. 4,116,626, 5,136,520, 5,142,481, and 5,208,592, the teachings of which are hereby incorporated by reference.
In the RECIRC devices and techniques described in the above-referenced U.S. patents, the substrate pattern is defined in terms of pixels, and individual colorants or combinations of colorants are assigned to each pixel in order to impart the desired color to that corresponding pixel on the substrate. The application of such colorants to specific pixels is achieved through the use of many individual dye applicators, mounted along the length of the various color bars that are positioned in spaced, parallel relation across the path of the moving substrate to be patterned. Each applicator in a given color bar is supplied with colorant from the same colorant reservoir, with different color bars being supplied from different reservoirs, typically containing different colorants. By generating applicator actuation instructions that accommodate the fixed position of the applicator along the length of the color bar as well as the position of the color bar relative to the position of the target pixel on the moving substrate, any available colorant from any color bar may be applied to any pixel within the pattern area on the substrate, as may be required by the specific pattern being reproduced. As will be appreciated by those skilled in the art, compensation for substrate travel time between rows must be provided.
Although patterning systems employing this RECIRC design have been successful, those familiar with such systems are aware of several consequences of the fundamental design that have to be accommodated for best results. These consequences arise as a result of the dye stream being formed continuously rather than as demanded by the pattern. This design feature results in a dye stream that (1) must be deflected onto the substrate in accordance with pattern data, and (2) must, at other times, be recirculated in order to minimize the consumption of expensive dyes.
The first design consequence (i.e. the deflection of the dye stream) results in the dye stream being subject to both a slight velocity component as well as certain fluid mechanical effects as the dye stream is first allowed to strike the substrate and then, as dictated by pattern data, is re-deflected into the catch basin. These effects, which can have a subtle, but perceptible effect on pattern definition in the form of a slightly elongated drop footprint along the axis of deflection (which also corresponds to the axis of conveyor motion) that would not be present if the dye stream were simply dispensed from an overhead applicator in “on/off” fashion.
Additionally, because control of the dye stream is indirect in the sense that it depends upon the control imposed on and by the transverse stream of deflecting fluid, this design sets inherent limitations on the minimum quantity of dye that can be accurately and reliably delivered to a specific pixel.
Similar to the issue discussed in connection with the DOD device, above, there is also the fact that the formation of a line that is parallel to the direction of substrate movement involves the ability to deflect the dispensed dye stream(s) at the exact time necessary to form a series of pixels that are in precise alignment as the applicator dispenser is moving perpendicular to the line being formed. Perhaps because of one or both of these possible effects, the pattern features produced by the RECIRC device are also known to be significantly anisotropic (i.e., direction-sensitive).
The second design consequence (i.e., the recirculation of the dye when not patterning) results in a limitation as to the chemical agents that can be added to the dye—the inclusion of surfactants, shear-sensitive thickening agents, etc. to the dye, for example, can result in undesirable behavior of the dye as it recirculates. An additional consequence of the re-circulation system is the need to incline the system to promote gravity-assisted draining of the catch basin. That inclination tends to cause freshly deposited dye to flow down the inclined substrate and can result in the occurrence of non-circular dye drops. Perhaps most fundamentally, these two design consequences—particularly the second—do not accommodate the use of high viscosity dyes, which traditionally are the dyes of choice for high definition patterning of textile substrates because of their reduced tendency to spread uncontrollably when applied, as compared with lower viscosity dyes of the same kind.
In a third approach (the “screen print” approach), a series of screens (typically, one per color) comprised of individual relatively fine-gauge meshes are placed, sequentially and in registration with preceding screens, directly over the area of the substrate to be patterned. Within each screen are locations where the screen mesh is occluded or blocked, so that when dye is applied to one side of the screen, it passes through and colors the substrate everywhere except at those locations.
Screen printing, while capable of a high degree of detail and definition, nevertheless has a process “signature” which tends to characterize textile substrates that have been patterned using this process. The physical dimensions of the screens themselves usually define, and limit, the size of the pattern repeat. Typically, the screen is placed into direct contact with the surface of the substrate being patterned. This not only can deform the face fibers, but also limits the success with which substrates having contoured or otherwise uneven top surfaces (e.g., non-level loop carpets) can be patterned. Due to this physical interaction with, and occasional displacement of, the surface fibers, as well as the difficulties associated with achieving close registration tolerances when dealing with the precise positioning of a series of large screens on a deformable surface having a high degree of texture, screen printing procedures normally provide for significant overlap (and, therefore, significant overprinting) between adjacent screen placements, to assure that no substrate within the boundary regions between adjacent screen positions will be underdyed. The visual consequences of this overprinting are frequently apparent.
Perhaps the most characteristic quality of screen printed products is the physical depth of the resulting dyed pattern. In order to provide adequate control of the placement of the dye as it is pressed through the screen, the dyes used tend to be high viscosity. The use of high viscosity dye allows for high definition images—such dyes are not normally prone to migrate, and minimizing lateral dye migration on the substrate tends to sharpen the dye boundaries on the substrate. However, minimizing lateral dye migration also tends to impede vertical (i.e., along the fiber) dye migration into the pile, which means that, although screen dyed products may appear rather detailed, they generally will not exhibit a high degree of dye penetration—dyed yarns in pattern regions will be completely dyed over perhaps the first 30 or 40 percent of their length (depending upon the composition and total overall length of the fibers comprising the pile face), beyond which dye penetration is usually quite non-uniform and frequently non-existent.
In summary, the carpet patterning systems of the prior art collectively suffer from several important shortcomings, including an inability to provide a product with high pattern definition or resolution that can be easily patterned from an unlimited number of unpatterned stock substrates, and that exhibits a wide variety of visually uniform colors (including in situ blended colors) that extend deep within the substrate face.